Screw and nut actuating mechanism



July 6, 1948, T. w. vlcKERs SCREW AND NUT ACTUATING MECHANISM 3Sheets-Sheet 1 Filed April 9 1945 @www N mm E am .E Y mm M x N mw T. w.vlcKERs 2,444,886

SCREW AND NUT ACTUATING MECHANISM 3 sheets-Sheet 2 July 6, 1948.

Filed April?, 1945 ATTORNEY Plantea Julye, `194e. l. l 2,444,886

\ UNITED uSTATES PATENT OFFICE v 2,444,886 l SCREW AND NUT ACTUATINGMECHANISM Theodore W. Vickers, Los Angeles, Calif.`

Application April 9, 1945, Serial No. 581,246 12 Claims. (Cl. 'I4-459)This'invention relates generally to mechanical direction wherein theyare caused to feed through movements and more particularly to actuatingthe screw and nut grooves by pressure of 'the mechanisms such as screwand nut operated load, so that in order for the load to driveA themechanisms employed in aircraft actuators, liftmechanism, the balls willbe forced to slide rather ing jacks, vises, presses and other screwdevices o than roll in the grooves, wlththe resulting greatly by whichan applied force is greatly multiplied increased friction between thescrew and nut beat 'a load. ing suilicient to support the load.

Although actuating mechanisms such as the It is a further object of thisinvention to proscrew and nut, and worm and gear have a highA vide amechanism of the above described characmechanical advantage,` thesliding friction bel ter, which, in its application to an aircraftactuatween the threads or teeth of the screw and tor or other devicesubjected to a load in two those of the nut or gear is very great, thusmakopposed directions, will be automatically operable ing suchmechanical movements extremely into obstruct rolling movement of theballs in the eilicient because of the relatively large frictionalgrooves of the screw and nut in one direction or loss. To reduce thisfriction to a relatively small l the other according as the load isimposed upon amount, a mechanism known as the ball bearing the mechanismto drive same in one direction screw nut has been developed and employsa or the other, so that the sliding friction thus proseries of ballsin'place of screw threads, which vided between the screw and nut willsupport the balls are forced to roll in mating helical grooves load, allwhile enabling the driving force to accr races in the screw and nut, byload pressure 2o 'cuate the mechanism in either direction in cpimposedthereon when working, and are byposition to the load with the ballsVfree to roll and passed from the grooves through the nm, and thusreduce the friction between the screw and returned to the grooves so asto circulate freely nut for high efficiency operation of the mechin onedirection or the other according as relaanism.

tive axial movement of the screw and nui; in one It is a still furtherobject of this invention to direction or the other is effected underload'. provide a control means for a. nut and screw or This ball bearingscrew nut mechanism elimisimilar actuating mechanism by Wlllell nlenates the thread-sliding friction by substitutingstrleted Circulationmay be effected under the therefor the rolling friction of the balls,thus pressure 0f a load in excess of a predetermined vastly increasingthe efnciency of the mechanism maximum 10nd immevably Slipperted by thewhile retaining its 'mechanical advantage. mechanism, so as tocompensate for sudden or However, this ball bearing nut mechanism hasheavy load shocks which might otherwise impose the disadvantagethat uponremoval of the drivdemeglng Crushing StreSSeS 0n the bellS- AlSO,

ing force therefrom, the load will act through the load can be renderedfree to drive the mechtheballs to drive the mechanism in a retrogradeansm and thus move at a predetermined rate direction because of the lackof friction between upon removal of the driving force from the mechthescrew and nut. To prevent such overhau enSIn, all t0 the end 0f greatlyextending the A of the mechanism, a holding force must be conrange ofuse of the mechanism. I

tinuously applied thereto, `or g, braking device With these and otherobjects in view, the inprovided in order to support the load. 40 ventionresides in the combinations, arrange- The primary object of this.invention is to proments and functional relationships of elements videa, ball bearing screw nut mechanism or simias set forth in the followingspecification and positive means by which the driving of such In theaccompanying drawings,

mechanism in a retrograde direction by the load Figure 1 is alongitudinal sectional view of an is prevented by interposing sufficientsliding fricaircraft actuator, with one form `of mechanism tion betweenthe screw and nut for the load to embodying this invention, appliedthereto and be supported without the use of a holding force, occupyingone active position;

braking, or other extraneous device. Figure 2 is an enlarged fragmentarylongitudi- Morespecifically, it isan object of this invennal sectionalview showing a portion of the airtion to provide a ball bearing screwnut or simicraft actuator with the mechanism embodying lar actuatingmechanism embodying means by this inventionv occupying another activeposition;

by the load is prevented by stopping the relatively views taken,respectively, on the lines 3 3, 4-4 frictionless rolling movement of theballs in the and 5-5 of Figure 2;

lar actuating mechanism embodying simple and particularly pointed 011i?ln the appended Claims.

which the retrograde drivingof such-mechanism Figures 3, 4 and 5 are'transverse sectional Figure 6 is a vertical longitudinal sectional tweenthe elements s and N which is nlled with view of a lifting Jack withanother form of mecha series of hardened steel balls Il providing ananism embodying this invention applied thereto; operative connectionbetween the elements which and functions in the manner oi a screw threadto Figure 7 is a transverse sectional view taken 5 relatively feed theelements axially 1n response on the line 1-1 of Figure 6. torotation ofthe screw element S.

Referring specifically to the drawings, and When the screw element 8 isbeing driven in illustration, embodied in an aircraft actuator 10 theattaching eyes Il and Il, or move them a screw element S. thus obtainedwith a minimum frictional loss. The screw element S is in the form of ashaft as the balls provide relatively small rolling fric- |2, one end ofwhich is iournaled in the casing tion between the screw and nutelements, rather Il is adapted to be driven in one direction or ballbearing screw nut mechanism has the disthe other by a reversibleelectric motor M whose advantage that the load being moved will as fieldIl is supported in the casing, and whose readily drive the mechanism ina retrograde div armature Il and commutator I1 are fixed on a rection byovercoming the slight rolling friction tubular shaft I8 freely receivingthe shaft lo in of the balls, upon removal of the driving force co-axialrelation thereto, and Journaled in bearfrom the mechanism, thusrendering saine4 inings Il and 2li supported by plates 2| and 22 capableof immovably su the load in the shafts 2s and mesh with a large gear 21fixed of the load, all of Awhich adds ally to the to the shaft to theend of providing a speedcost and upkeep of the mechanism, reducing geartrain between the armature shaft o overcome the disadvantage thisinvention eans at a slow speed relative to that of the motor M.preferably co-eeiing directly with the balls l0 The nut element N iscomposed of two secand comprisingin one embodiment, pawls or dogs tionsand 2i. the section 30 being in the form 30 and DiVOtil-llv mvllnted byRTCW! 2 and of a cylindrical body havinga longitudinal bore I3 0n theplate l1 at opposite sides of the ball I2 of a slightly larger diameterthan that of the 4U Conduit i., and urged by springs Il and t0 ceivingthe shaft is, whose outer end is Jour- The pawls are disposed in opposedrelationship posed and alined relation to the attaching eye are required1n the use 0f the invention on an The section 30 is mounted between theheads a load imposed thereon sometimes in one di- 34 and 35 byanti-friction bearings I0 and 4| rection, and Bt other time# 111 the099081150 difor axial movement with the section. as a reiion singleunit, and is provided with keys 42 co-act 55 Cil-acting with therespective pawls III and 0| con a lost motion rotational drivingconnection (Fignection provided between thev sections 2| and ure 3)between the sections 30 and 3| for a pur- 3| of the nut element N by thekeys 42 and keypose to be later described. ways 43, are actuating lugsin the form of pins The wall oi the bore 32 in the section 30 of 60 10and 1| projecting from the barrel Il o! the the nut element N isprovided with a helical section 2| for actuation of the respective pawlsThe ends of the groove 50 are closed on' from 65 the section It tends torotate relative to the the ends of the section 30 by two opposite]section 2| in one direction or the other in the sitioned ring segments52 and 53 seating tightly operation of the invention which is as followsin the groove so as to provide a plurality of inith one o e eyes and Ilanchored to volutions communicate at the ring segments 52 7o moved inadirection separating the eyes. the

posed ball conduit Il formed in plate -51 secured direction of the arrowin Figure 1. thus tending by screws la on a dat face of the section 3o,all to cause the balls 5l to circulate through the ball to the end ofproviding a continuous ball race berace in the direction of the arrow.It will be shown in Figure 2 by the arrow in Figure by the drivingforce. This,

noted that under this. condition. the pawl ll has been moved by. the pinIl to its inactive position. whereas the pawl il is freed of itspin 1lso as to be yleldingly urged by its spring et to its active position,all during the initial slight rotation of the section 3l relative tothesection Il permitted by the lost motion driving connection between thekeys 42 and keyways u, following which the nut element N will be movedto the right in Figure l as the balls freely click past the bill of theactive pawl ll in the direction of the arrow, under the pressure imposedby the driving force on those balls in the grooves l and il. Therefore,it will be evident that the high mechanical advantage of the screw andnut will be obtained, with an attending high emciency duetothenegligible rolling friction provided by the ballsbetween the screw andnut elements.

^ lHowever. upon removing the driving force from the screw element S thepressure imposed on the balls in the grooves l0 and Il by the resistancef of the load, will be reversed, thus tending to circulate the balls inthe direction reverse to the arrow, which circulation is positivelyprevented by the active pawl Il. As the tendency of the nut element N torotate the screw element S in a retrograde direction. is resisted by thelarge sliding friction of the now non-circulating balls between theelements, rather than the small rolling friction present when thedriving force was applied, the load will be supported in the position towhich it has been moved.

Assuming that the loadcondition is reversed and acts in the oppositedirection by tending to separate the eyes Il and 39, the pawls CII andIl will be reversed automatically to `the positions the slight initial`reverse rotation of the element Il permitted by the lost motion drivingconnection between the keys 42 and keyways so that in response todriving the nut element N in the direction opposite to A 1 -to feed thenut element towards the left, the balls Il will circulate in thedirection of thearrow in Figure 2 by freely clicking past the now activepawl Il. Upon removing the driving force from the screw element, thereverse circulation. ofthe balls by the load will be prevented bythepawl Il withthe advantages above described.

It will be noted that the bills of the pawls 60 and 8l can .be so shapedas to permit a restricted circulation of the balls by sudden or heavyloads in excess of a predetermined maximum load, so as to preventdamaging'crushing stresses from being imposed on the balls bysuch-excessive loads, all without adversely affecting the functioning ofthe balls in co-action with the pawls to support loads up to thepredetermined maximum.

^ Furthermore, springs of; different strengths could be utilized forthis purpose in order to compensate for excessive load shocks.Considering that surface of the pawl being engaged by theballs, as aninclined plane or a cam, it will be appreciated that by reducing to rapredetermined inclined plane, the angle of the surface of the activepawl whichis being engaged by the balls to stop their circulation by lsuch surface bythe balls will be effected, so as to tendV to move thepawl` to inactive position against the pawl spring, which latter, undersuch condition is made of such strength to inefiectively opposemovement'of the pawl to inactive position bythe balls, and thus permitthem to continue to roll but not so freely as in the direction caused ineffect. is a brake a suitable crank handle l to be attached to drive thescrew element through `the screw element S',

placed upon the flow' of the balls through the bypass, and thus abrake-on the "overha of the screw nut.

It will be clear from the foregoing description that regardless ofwhether the screw element S is being driven in one direction oroppositiorrto a load, the negligible rolling friction of the b; lls Siwill be utilized, and that upon removal of the driving force, one pawlor. the other will automatically co-act with the balls to substitute thesliding friction for the rolling friction thereof in order to supportthe "load,

Reference will now be had to Figures v6 and I in which is illustrated asecond `embodiment of this invention which can be applied to the liftingjack shown, or to a vise. press, or other device in which the loadalways acts in one direction.

The lifting jack comprises a base Il having a tubular standard Il inwhich is vertically slidable a plunger 82 havinga load-engaging head Il,and being secured to a nut element N co-acting with a screw element S'.The screw element is'in the form of a cylindrical shaft 84 rotatablymounted in the standard by a thrust bearing 'IB and a central retainingscrew 86. Fixed to the screw element is a relatively large gear l'l withwhich meshes a pinion gear 88 journaled inthe 'standard 8l and having anon-circular shank 89 to which (not shown) is adapted the gears.

The longitudinal bore l32a of the nut element,

N' is of a slightly larger diameter than that of and is provided with ahelical groove Na co-acting with a' mating helical groove ila in theportion of the screw element which is adapted to be traveled upon by thenut element. The ends of the groove lila are closed oi from the ends ofthe nut element by two oppositely positioned ring segments 52a and aseating tightly in the groove so as to provide a plurality ofintervening convolutions. The ends of these vconvlolutions communicateat the ring segments with tangential ball conduits a and lla in the nutelement N', connected by an obliquely disposed ball conduit a formed ina plate 51a secured by screws 58a on a ilat face of the nut element, allto the end of providing a continuous ball race between the elements Si'and N' which is filled with balls ita providing an operative connectionbetween the elements in the manner previously described.

the load, a camming action upon A single dog or pawl a is reciprcablymount- Y ed in abore in the nut element N', and is urged to the activeposition shown in Figure 6, by a coil spring Bla working in nutelement', and bearing at one end against the head 93 of the pawl. and-atits other end against an adjustable pressure screw bore 92 and locked inadjusted position by a )am nut 95. Under the action of thespring "a, theworking end of the n slot 66a in the ball conduit 56a into the path ofmovement of the balls therethough. The working end of the pawl isprovided with a stop shoulder 96 to prevent circulation of the balls inthe.

direction caused by the load. and is provided with a, cam -surface 91 topermit the balls to freely pass the pawl in the opposite directioncaused by the driving force applied to the screw element in oppositionto thev arrows in Figure 6.

Thus, the plunger 82 will be raised by utilizing the relatively smallrolling friction of the freely circulating balls between the screw andnut elethe other in v an enlarged bore l2 of the j threaded in the pawlBla projects through a.

load, `as is indicated by the` 1 elements-for relative .7 ments. andwill be eifectivelysupported against lowering movement or retrogradedriving of the mechanism by the largel sliding friction ofnoncirculating balls.

A release member in the form of a pull rod Illil,

extends through a longitudinal bore in the screw in the case oi anautomobile jack.

It will be evident that by varying the shape of the stop shoulder 96 sothat it presents a less abrupt steeply inclined surface to the balls59a, and byvarying the loading of the spring 84a with the pressure screw94, restricted circulation of the excessive loads. Under this condition,the stop shoulder 9B functions as an inclined cam surface I claim: 1;Inmechanism of the* class described, two elements having co-actinghelically related grooves; balls in said grooves operatively connectingsaid elements for relative movement, one g v by the other;

provide a means co-actlng with said grooves to support the load; andmeans co-acting with the balls to free them for rolling movement whennecting said elements for relative movement, one by the other; meansco-acting with said grooves to provide a continuous circulatory pathalong which thelballs are forced to roll in one `direction 8 forced torollin' one direction or the other according as axial pressure isimposed in one direction or the other in said grooves oppositedirection.

4. In mechanism of thel class described. two elements having co-actingheiically related grooves; balls in said opposition to a load, or in theother direction by the load; means co-acting with the balls to preventcirculation thereof in that direction caused imposed dn the load shocks.

5. In mechanism of the class 6. In mechanism of the class described, two

velements having mating helical grooves: balls in said groovesoperatively connecting said elements to permit circulation of the ballsin the reverse direction.

7. In mechanism of the class described, screw and nut elements havingmating helical grooves;

elements forrelative movement, one by the other;

ball conduit in the nut element. co-acting with said grooves to providea continupath along which the balls are forced to roll in one directionor the other according assaid relative movement of the elements iseffected in one direction in opposition or in the other direction by theload;

said conduit; means urging said pawls to an active position wherein theyrespectively prevent circulation of the balls in opposite directions;andmeans lcio-acting with the pawls to maintain one inactive while theother is active, so as to permit circulation of the balls in thedirection opposite to that-in which circulation of the balls is beingpreventedby the active pawl.l

8. In mechanism of the yclass described, screw and nut elements, thelatter being composed of two sections operativelyconnected by a lostmotion' rotational driving connection and for axial .movement as a unit;said screw element and one of said sections having mating helicalgrooves; balls in said groovesoperatively connecting said screw elementand'said one section for relative axial moycmentl of the sections inresponse to relative rotation of the elements; means co-acting with saidgrooves to provide a continuous circulatory path along which the ballsare forced to roll in one direction or the other according as said axialmovement of the elements is effected and nut elements, the latter beingcomposed of two sections operatively connected by a lost motionrotational 4driving connection and for axial movement as a unit; saidscrew element and one f of said sections having mating helical grooves;

balls in said grooves operatively connecting said screw element andsaidone section for relative axial movement of the sections in response torelative rotation of the elements; means co-acting with` said grooves toprovide a continuous circulatory pathv along which the balls are forcedto roll in one direction or the other according as said axial movementof the elements is effected in one direction or the other under load;two pawls; means urging said pawls to an active position wherein theyrespectively co-act with the balls in preventing circulation thereof inopposite directions; and means on said other nut section for moving onepawl or the other to an .inactive position according as the rotationbetween the elements permitted by said lost motion connectiontherebetween is effected in one direction or the other,

10. In mechanism of the class described, two elements having co-actinghelically related grooves; balls in said grooves operatively connectingsaid elements for relative movement, one by the other: means co-actingwith said grooves to provide a continuous circulatory path along whichthe balls are forced to roll in one direction or the other according assaid relative movement of the elements is effected in opposition to aload, or in the other direction by the load; a pawl; means urging Isaidpawl to an active position wherein the pawl will co-act with the ballsin preventing their circulation in that direction caused by the load, soas to utilize sliding friction of the balls between the elements, insupporting the load; and means by which said pawl can be moved to aninactiveposition so as to restore the rolling friction of the ballsbetween the elements for retrograd Vmovement thereof by the load.

11. In mechanism of the class described, two elements, one of which isLadapted to be driven for co-actionk with the other in moving a load; aseries of balls; means defining a continuous race between said elementsreceivingsaid balls to operatively connect the elements for relativemovement through the medium of the balls which are forced to circulatein one direction or the other according as said relative movement of theelements is effected in one direction in opposition to a load, or in theother direction by the load; a movably mounted pawl adapted to co-actwith said balls; and means yieldingly uging said pawl to an :activeposition wherein said pawl will prevent circulation of the balls in onedirection.

12. In mechanism of the class described, two elements, one of which isadapted to-be driven for co-action with the other in moving a load; aseries of balls; means defining a continuous race between said elementsreceiving said balls to operatively connect the elements for relativemovement through the medium of the balls which are forced -to circulatein one direction or the other according as said relative movement of theelements is effected in one direction in opposition to a load, or in theother direction by the load; a movably mounted pawl adaptd to co-actwith said balls; and means yieldingly urging said pawl to an activeposition wherein said pawl will retard circulation of the balls in saidother direction to a predetermined extent. yet render the ballsrelatively free to circulate in said one direction.

THEODORE W. VICKERS.

REFERENCES CITED UNITED STATES PATENTS Name Date Coughlan Oct. 4, 1898Number

